1. Field of the Invention
The present invention relates to mobile communication terminals and to control methods therefor.
2. Related Art
In recent years, OFDM (Orthogonal Frequency Division Multiplexing) has attracted attention as a radio communication method for mobile communication systems, as disclosed in, for example, Patent Documents 1 and 2 below. Compared with other communication methods (e.g., Time Division Multiplexing, Frequency Division Multiplexing, Code Division Multiplexing, etc.), OFDM has advantages such as higher efficiency of frequency utilization and higher resistance to multipath interference. OFDM is a carrier transmission method in which a single frequency band is divided into multiple subcarriers that are orthogonal to each other, and in which data is transmitted on each subcarrier. Generally, in OFDM, a received signal is demodulated using FFT (fast Fourier transform). Since FFT requires an enormous amount of computing, power consumption for FFT is also enormous.
In a mobile communication system such as a cellular phone system, it is important to minimize power consumption in a mobile communication terminal. This is because the battery will be drained more rapidly and the battery standby time will be shorter if power is wasted. As a result, the terminal must include a larger battery to provide sufficient battery standby time.
In order to reduce the power use of a mobile communication terminal, there have been proposed techniques in which the electricity supply is suspended when the terminal is not in communication. For instance, Patent Document 3 below discloses a technique in which power is switched on and off depending on the status of the terminal. This technique enables the terminal to reduce power use by determining time periods in which the terminal will not communicate and by stopping the electricity supply during the determined time periods.    Patent Document 1: JP-A-2008-236154    Patent Document 2: JP-A-2007-174353    Patent Document 3: JP-A-2004-172982
Mobile communication terminals have been steadily reduced in size and weight. Thus, there is a problem with convenience of use if a large battery is used to provide long battery standby times or if multiple batteries must be carried. In order to ensure convenience of use, the size of the battery is preferably reduced by reducing the consumption of power for FFT.
In the above-described technique, the electricity supply is stopped when the terminal is not communicating. The mobile communication terminal used with the technique connects to a base station periodically to determine whether or not there is an incoming call. However, since the electricity supply is suspended when the terminal is not communicating with the base station, the terminal requires time for reactivation and cannot respond immediately to the base station when the base station accesses the terminal.